Methods and instruments for interbody fusion

ABSTRACT

A laparoscopic surgical technique is provided for preparing a site for implantation of a novel fusion device or implant. In accordance with one embodiment of the technique, a laparoscope is provided having an outer sleeve with distraction fingers at one end to distract the disc space. The laparoscope provides a sealed working channel to the disc space, through which the disc space is distracted, the vertebral endplates and surrounding disc is reamed, and the fusion device inserted. A distraction plug is provided for centering the outer sleeve and for providing midline distraction of the disc space. In one embodiment, a fusion device includes diverging bone screws passing through an end wall and upper and lower walls of the device to engage the adjacent vertebrae. In another embodiment, a connector plate is engaged to bilaterally position fusion devices to prevent rotation and resist expulsion of the devices from the disc space.

REFERENCE TO RELATED APPLICATIONS

This is a divisional application of co-pending U.S. patent applicationSer. No. 09/014,901 filed Jan. 28, 1998, now U.S. Pat. No. 6,206,922which is a continuation-in-part of U.S. patent application Ser. No.08/604,874, filed Feb. 22, 1996, now abandoned which is acontinuation-in-part of U.S. patent application Ser. No. 08/411,017,filed Mar. 27, 1995, now U.S. Pat. No. 5,782,919 all owned by theassignee of the present application.

BACKGROUND OF THE INVENTION

The present invention relates to methods and instruments for performingan interbody fusion of a disc space between two adjacent vertebrae.Specifically, the invention concerns laparoscopic techniques andinstruments to prepare a fusion site and to insert fusion devices andimplants.

The number of spinal surgeries to correct the causes of low back painhas steadily increased over the last several years. Most often, low backpain originates from damage or defects in the spinal disc betweenadjacent vertebrae. The disc can be herniated or can be suffering from avariety of degenerative conditions, so that in either case theanatomical function of the spinal disc is disrupted. The most prevalentsurgical treatment for these types of conditions has been to fuse thetwo vertebrae surrounding the affected disc. In most cases, the entiredisc will be removed, except for the annulus, by way of a discectomyprocedure. Since the damaged disc material has been removed, somethingmust be positioned within the intradiscal space, otherwise the space maycollapse resulting in damage to the nerves extending along the spinalcolumn.

The intradiscal space is often filled with bone or a bone substitute inorder to prevent disc space collapse and to promote fusion of the twoadjacent vertebrae. In early techniques, bone material was simplydisposed between the adjacent vertebrae, typically at the posterioraspect of the vertebrae, and the spine column was stabilized by way of aplate or a rod spanning the affected vertebrae. Once fusion occurred thehardware used to maintain the stability of the segment becamesuperfluous. Moreover, the surgical procedures necessary to implant arod or plate to stabilize the level during fusion were frequentlylengthy and involved.

It was therefore determined that a more optimal solution to thestabilization of an excised disc space is to fuse the vertebrae betweentheir respective end plates, preferably with the need for anterior orposterior plating. There have been an extensive number of attempts todevelop an acceptable intradiscal implant that could be used to replacea damaged disc and maintain the stability of the disc interspace betweenthe adjacent vertebrae, at least until complete arthrodesis is achieved.These “interbody fusion devices” have taken many forms. For example, oneof the more prevalent designs takes the form of a cylindrical implant.These types of implants are represented by the patents to Bagby, U.S.Pat. No. 4,501,269; Brantigan, U.S. Pat. No. 4,878,915; Ray, U.S. Pat.Nos. 4,961,740 and 5,055,104; and Michelson, U.S. Pat. No. 5,015,247. Inthese cylindrical implants, the exterior portion of the cylinder can bethreaded to facilitate insertion of the interbody fusion device, asrepresented by the Ray, Brantigan and Michelson patents. In thealternative, some of the fusion implants are designed to be pounded intothe intradiscal space and the vertebral end plates. These types ofdevices are represented by the patents to Brantigan, U.S. Pat. Nos.4,743,256; 4,834,757 and 5,192,327.

Interbody fusion devices can be generally divided into two basiccategories, namely solid implants and implants that are designed topermit bone ingrowth. Solid implants are represented by U.S. Pat. Nos.4,878,915; 4,743,256; 4,349,921 and 4,714,469. The remaining patentsdiscussed above include some aspect that permits bone to grow across theimplant. It has been found that devices that promote natural boneingrowth achieve a more rapid and stable arthrodesis. The devicedepicted in the Michelson patent is representative of this type ofhollow implant which is typically filled with autologous bone prior toinsertion into the intradiscal space. This implant includes a pluralityof circular apertures which communicate with the hollow interior of theimplant, thereby providing a path for tissue growth between thevertebral end plates and the bone or bone substitute within the implant.In preparing the intradiscal space, the end plates are preferablyreduced to bleeding bone to facilitate this tissue ingrowth. Duringfusion, the metal structure provided by the Michelson implant helpsmaintain the patency and stability of the motion segment to be fused. Inaddition, once arthrodesis occurs, the implant itself serves as a sortof anchor for the solid bony mass.

Another interbody fusion device that is designed to permit bone ingrowthis shown in FIG. 1. This device is described and claimed in co-pendingparent application Ser. No. 08/411, 017, filed on Mar. 27, 1995, whichdisclosure is incorporated herein by reference. In one embodiment, thisinvention contemplates a hollow threaded interbody fusion device 10configured to restore the normal angular relation between adjacentvertebrae. In particular, the device 10 as shown in FIG. 1 includes anelongated body 11, tapered along substantially its entire length,defining a hollow interior 15 and having a largest outer diameter at theanterior end 12 of the device to receive the bone growth material. Thebody 11 includes an outer surface 16 with opposite tapered cylindricalportions and a pair of opposite flat tapered side surfaces 22 betweenthe cylindrical portions. Thus, at an end view, the fusion device givesthe appearance of a cylindrical body in which the sides of the body havebeen truncated along a chord of the body's diameter.

The cylindrical portions include threads 18 for controlled insertion andengagement into the end plates of the adjacent vertebrae. A startedthread 19 is provided at the posterior end 13 of the device 10 tofacilitate engagement within a prepared bore. The outer surface of thisfusion device is tapered along its length at an angle corresponding, inone embodiment, to the normal lordotic angle of the lower lumbarvertebrae. The outer surface is also provided with a number ofvascularization openings 24, 25 defined in the flat side surfaces, and apair of opposite elongated bone ingrowth slots 27 defined in thecylindrical portions.

Various surgical methods have been devised for the implantation offusion devices into a subject disc space. A patent to Dr. GaryMichelson, U.S. Pat. No. 5,484,437, discloses one such technique and theassociated instruments. As described in more detail in that patent, thesurgical technique involved the use of a hollow sleeve having teeth atone end that are driven into the adjacent vertebrae. These teeth and thesleeve maintain the disc space height during the subsequent steps of theprocedure. In accordance with one aspect of the invention in the ‘437patent, a drill is passed through the hollow sleeve to remove the discand bone material to produce a prepared bore for the fusion device. Thedrill is then removed from the sleeve and the fusion device ispositioned within the disc space using an insertion tool.

In another aspect of the procedure and instruments disclosed in the ‘437patent, a long distractor is provided having penetrating portions thaturge the vertebral bodies apart to facilitate the introduction of thenecessary instruments. The long distractor can act as a guide fordrilling and reaming tools concentrically advanced over the outside ofthe distractor to prepare the site for the fusion device.

While the Michelson technique represents a significant advance overprior surgical procedures for the preparation and insertion of fusiondevices, the need for improvement remains. In particular, procedures andinstruments that preserve the integrity of the surgical site aredesirable. The present invention is directed to this need in the field.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a novel fusion device isprovided that integrates a pair of bone screws. The fusion device can bea hollow substantially cylindrical body, such as the device shown inFIG. 1. In this aspect, the device includes a pair of screw bores formedin an end face of the body. The bores are arranged so that bone screwsextending through the bores will be driven into the endplates of theadjacent vertebrae. In certain features, the heads of the bone screwsare recessed within the body and held in place by a connon lockingscrew. The screws help prevent retrograde expulsion or rotation of thefusion device, or a spacer, from the disc space.

The present invention also contemplates another approach to preventingrotation and/or dislodgment of fusion devices placed bilaterally in thedisc space. In one embodiment, a transverse connector plate is engagedby locking screws to the end walls of the bilateral fusion devices. Inone feature, the end walls defme central recesses and transverse groovesto receive the connector plate. In another embodiment, the connectorplate can include screw bores to receive bone screws driven into thevertebrae at a location in between the fusion devices.

In another aspect of the invention, a method is provided for preparing asubject disc space for implantation of a fusion device or implantbetween adjacent vertebrae. In this technique, a laparoscope is providedthat includes an outer sleeve with opposite extensions at one end of theouter sleeve and a laparoscopic port engaged at the outer end of theouter sleeve, the laparoscopic port having a number of seals, with theopposite extensions configured to maintain distraction of the adjacentvertebrae.

The preferred technique comprises the steps of making an incision in theskin of the patient aligned with the subject disc space, retractingtissue beneath the incision to expose the disc annulus; and piercing thedisc annulus to create an opening. The outer sleeve of the laparoscopeis advanced through the incision, leaving the port outside the skin ofthe patient while inserting the opposite extensions into the disc spacewith the outer sleeve contacting the disc annulus. The laparoscope, andparticularly, the outer sleeve, creates a protected working channelbetween the disc space and the laparoscopic port outside the patient.

In a further step of the preferred inventive technique, a reamer isoperated through the number of seals and the outer sleeve of thelaparoscope to create a prepared bore in the disc material and theadjacent vertebrae for implantation of a device into the bore.

In a most preferred embodiment of the surgical technique, the techniquecomprises the steps of percutaneously exposing the annulus of the discin the subject disc space through an incision in the skin of the patientand piercing the disc annulus to create an opening. A distractor canthen be inserted through the incision and through the opening into thedisc space to distract the vertebrae adjacent the subject disc space.The laparoscope outer sleeve is then introduced through the incision andover the distractor, leaving the port outside the skin of the patientwhile inserting the opposite extensions through the opening into thedisc space to create the protected working channel between the port andthe distractor tip.

In subsequent steps, the distractor is removed and a reamer is advancedthrough the number of seals of the laparoscope and through the outersleeve into the disc space to ream the disc space and adjacent vertebraeto create a prepared bore for the fusion implant. After the reamer isremoved from the laparoscope, the fusion implant can be advanced throughthe number of seals and through the outer sleeve into the prepared bore.With the fusion implant in position, the laparoscope can be withdrawnfrom the patient.

In one aspect of the invention, a switching sleeve is placed within theouter sleeve of the laparoscope with an end of the switching sleeveprojecting beyond the opposite fingers of the outer sleeve, the end ofthe switching sleeve being tapered to minimize trauma to tissue adjacentthe subject disc space as the outer sleeve adjacent into the patientwith the switching sleeve projecting beyond the opposite extensions ofthe outer sleeve.

In a further embodiment, the laparoscopic method is used for bilateralplacement of two fusion devices into a subject disc space. In additionto the steps previously described, this embodiment of the surgicaltechnique includes unseating the outer sleeve of the laparoscope fromthe first opening in the disc annulus by withdrawing the laparoscopeuntil the opposite extensions of the outer sleeve are outside the discannulus. With the switching sleeve in position within the outer sleeve,the laparoscope is moved to the second opening in the disc space withoutremoving the laparoscope from the patient. The steps for preparing thebore to receive a fusion implant can be repeated. In one specificembodiment, these steps are conducted at the second opening with thedistractor remaining within the first opening. After a fusion implant isadvanced through the number of seals and through the outer sleeve intothe second prepared bores the laparoscope can then be returned to thefirst opening for insertion of another fusion implant. During this step,the fusion implant contained within the second prepared bore maintainsdistraction of the disc space.

As an adjunct to this inventive technique, a distraction device isprovided in one aspect of the invention. The distraction device caninclude an elongated stem sized for insertion along the A-P midline ofthe intervertebral disc space. Preferably, opposite surfaces of thedevice include a number of ridges that operate as bone engaging surfacesto resist expulsion of the device. In one important feature, the stem ofthe distraction device includes a bore to receive a spike projectingfrom a tubular body, such as the outer sleeve discussed above. With thisfeature, the distraction device acts not only as a midline distractor,but also as a centering guide to locate the tubular body through whichsubsequent surgical procedures can be performed.

In a further feature, the distraction device can include a flangeprojecting from the stem. The flange has a bone contacting thattransmits to the vertebra a force applied to the distraction device(preferably by a manual tool). This flange can be used to reduce a highgrade spondylolisthesis condition as the distraction device is driveninto the disc space.

One object of the present invention is to provide surgical technique andinstruments that permit the preparation of a disc space for insertion ofa fusion implant under a sealed condition. A further object of theinvention is to implement laparoscopic techniques to implant fusiondevices.

With respect to fusion devices, one object is to enhance the stabilityof the device in situ while reducing the risk of expulsion of thedevice. Yet another object is to provide means for readily reducing aspondylolisthesis condition from a laparoscopic approach.

One benefit of the present invention is that all of the steps necessaryto prepare a disc space and to implant a fusion device can be conductedin a protected environment. In addition, the inventive techniques andinstruments allow minimal intrusion into the patient, which minimizedthe risks normally associated with spinal surgery.

Other objects and benefits can be discerned from the following writtendescription and accompanying figures.

DESCRIPTION OF THE FIGURES

FIG. 1 is a side perspective view of a threaded fusion device having atapered configuration to restore the normal angle of a spinal motionsegment.

FIG. 2 is a top elevational view of an implant driver for use inengaging and driving a fusion device such as the device shown in FIG. 1.

FIG. 3 is an enlarged perspective view of the end of the implant drivershown in FIG. 2 engaged to a fusion device such as shown in FIG. 1.

FIG. 4 is an enlarged side cross-sectional view of the implant driverand fusion device shown in FIG. 3.

FIG. 5 is an enlarged side cross-sectional view of an alternativeembodiment of an implant driver for engaging and driving a fusion devicesuch as the device shown in FIG. 1.

FIG. 6 is a driving tool attachment according to one aspect of thepresent invention.

FIG. 7 is an enlarged side cross-sectional view similar to the view inFIG. 5 with the driving tool attachment of FIG. 6 engaged between theimplant driver and the fusion device.

FIG. 8 is an end perspective view of a threaded fusion device accordingto a further embodiment of the invention.

FIG. 9 is a side perspective view of a driving tool attachment accordingto a further aspect of the present invention in which the driving toolattachment is configured to engage the fusion device depicted in FIG. 8.

FIG. 10 is a side partial cross-sectional view of a fusion deviceaccording to the embodiment of FIG. 8 disposed between adjacentvertebrae and engaged in position by a pair of bone screws in accordancewith one aspect of the present invention.

FIGS. 11(a)-(d) are lateral representations of the spine showing foursteps of a surgical method for implanting a fusion device such as thedevice in FIG. 1 according to an anterior approach in one aspect of thepresent invention.

FIGS. 12(a)-(d) are lateral representations of the spine showing foursteps of a surgical method for implanting a fusion device such as thedevice in FIG. 1 according to a posterior approach in a further aspectof the present invention.

FIG. 13 is a frontal view of a patient with locations identified forsurgical incisions according to a preferred embodiment of the presentinventive laparoscopic surgical technique.

FIG. 14 is an A-P representation of a spinal segment at the laparoscopicsurgical site depicting one step of the inventive surgical technique inwhich bilateral locations are marked on the disc annulus for insertionof a pair of fusion devices, such as the device shown in FIG. 1.

FIG. 15 is an enlarged A-P view of the disc at the spinal segmentshowing the use of the template represented in FIG. 14 of the invention.

FIG. 16 is an A-P representation of the laparoscopic surgical sitedepicting a further step of the inventive surgical technique of creatinga pilot hole at each of the bilateral locations marked in the step shownin FIG. 14.

FIG. 17 is an A-P representation of the laparoscopic surgical sitedepicting a further step of the inventive surgical technique of using atrephine to create a bore at each of the bilateral locations marked inthe step shown in FIG. 14.

FIG. 18 is an A-P representation of the laparoscopic surgical sitedepicting a further step of the inventive surgical technique forinserting a distractor into the prepared site at each of the bilaterallocations marked in the step shown in FIG. 11.

FIG. 19 is a perspective representation of the laparoscope according tothe present invention in which the outer sleeve of the laparoscope isengaged within the subject disc space.

FIG. 20(a) is a perspective representation of the laparoscope of FIG. 19with a switching sleeve according to one aspect of the inventiondisposed within the laparoscope.

FIG. 20(b) is an enlarged A-P representation of the laparoscope andswitching sleeve of FIG. 20(a) showing the positioning of the distractortip as depicted in FIG. 18.

FIG. 21 is a perspective representation of the laparoscope of FIG. 19with a reamer extending through the laparoscope to prepare the site forreceiving a fusion device.

FIG. 22 is a perspective view of an implant driver of the type shown inFIG. 2 engaged to a fusion device and including a T-handle assemblyengaged to the driver.

FIG. 23 is a perspective view of an implant holder according to oneaspect of the present invention.

FIG. 24 is a perspective representation of the laparoscope used toimplant a bone dowel within the prepared site and including a bone dowelimpactor in accordance with one aspect of the present invention.

FIG. 25 is a top perspective view of a distraction plug in accordancewith one embodiment of the present invention.

FIG. 26 is a side cross-sectional view of the distraction plug shown inFIG. 25.

FIG. 27 is an end elevational view of the distraction plug shown inFIGS. 25 and 26.

FIG. 28 is a side view of the distraction plug shown in FIG. 25 as it isinserted between adjacent vertebrae using a plug driver in accordancewith one aspect of the present invention.

FIG. 29 is a side perspective view of a distraction plug in accordancewith a further embodiment of the present invention.

FIG. 30 is a side perspective view of a plug driver in accordance with afurther embodiment of the invention configured for engaging a distractorplug as shown in FIG. 29.

FIG. 31 is a rear perspective view of a percutaneous surgical sleeve inengagement with a distractor plug in accordance with the embodimentshown in FIG. 25.

FIG. 32 is a superior A-P view of a vertebra of the spine with thedistractor plug and percutaneous surgical sleeve shown in FIG. 31disposed within the disc space, with an alternative position of thesleeve shown in phantom.

FIG. 33 is a side perspective view of a percutaneous surgical sleeve inaccordance with a further embodiment of the invention with an outriggerspike engaged thereto for attachment to a distractor plug according toFIGS. 25 or 29.

FIG. 34 is an end perspective view of a double barrel percutaneoussurgical sleeve configured for engaging a distractor plug, such as thedistractor plug shown in FIG. 29.

FIG. 35 is a side perspective view of an assembly in accordance with afurther embodiment of the present invention utilizing a pair of fusiondevices connected by a connector plate.

FIG. 36 is a side perspective view of an alternative embodiment of theassembly with a pair of fusion devices interconnected by an alternativeconnector plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

As described above, one interbody fusion device, as shown in FIG. 1, canbe implanted within the intradiscal space. This interbody fusion device10 can be implanted using the implant driver 50 shown in FIG. 2. Theimplant driver 50 is comprised of a shaft 51 and sleeve 52concentrically disposed about the shaft. Tongs 54 are formed at one endof the shaft for gripping the interbody fusion device 10 forimplantation. Preferably the tongs include a tapered outer surface 55and an opposite flat inner surface 56 adapted to engage the truncatedside walls 22 of the interbody fusion device as shown in FIGS. 3, 4.Most preferably the tapered outer surface 55 conforms to the rootdiameter of the interrupted threads 18 of the device 10 so that thetongs 54 essentially complete the full cylindrical shape of the bodywall 16. The adaptation of the tongs' tapered outer surface 55facilitates screw insertion of the interbody fusion device 10 since theouter surface 55 will ride within the tapped bore in the vertebral endplates.

Each of the tongs 54 can be provided with interlocking fingers 58 and adriving projection 59 extending from the inner surface 56, most clearlyshown in FIG. 4. Referring again to FIG. 2, the shaft 51 defines a hingeslot 62 supporting each of the pair of tongs 54. The hinge slot 62 isconfigured so that the tongs will have a naturally biased positionspread sufficiently apart to accept the fusion device 10 therebetween.The shaft 51 defines a conical taper 63 between the hinged slot 62 andeach of the tongs 54. This conical taper mates with a conical chamfer 67defined on the inner wall of the sleeve 52. Thus, as the sleeve 52 isadvanced toward the tongs 54, the conical chamfer 67 rides against theconical taper 63 to close or compress the hinge slot 62. In this manner,the tongs 54 are pushed toward each other and pressed into grippingengagement with the interbody fusion device situated between the tongs.

The shaft 51 and sleeve 52 are provided with a threaded interface 65which permits the sleeve 52 to be threaded up and down the length of theshaft. Specifically, the threaded interface 65 includes external threadson the shaft 51 and internal threads on the sleeve 52 having the samepitch so that the sleeve can be readily moved up and down the implantdriver 50. The shaft 51 is also provided with a pair of stops 69 whichrestrict the backward movement of the sleeve 52 to only the extentnecessary to allow the tongs 54 to separate a sufficient distance toaccept the interbody fusion device 10.

The use of the implant driver 50 is shown with reference to FIGS. 3, 4.As can be seen in FIG. 3, the outer surface 55 of the tongs 54 residegenerally flush with the root diameter of the interrupted threads 18. Asseen in FIG. 4, the interlocking fingers 58 can be arranged to fitwithin the vascularization opening 24 on each of the truncated sidewalls 22. In a similar fashion, the driving projections 59 engage thedriving tool slots 29 at the anterior end 12 of the conical body 11. Thecombination of the interlocking fingers 58 and driving projections 59firmly engage the interbody fusion device 10 so that the device can bescrew threaded into a tapped or untapped opening in the vertebral bone.The tongs 54 in this embodiment are configured to engage the fusiondevice 10 and to impart a threading or rotational force to the device.It is understood that the tongs can adopt other configurations dependingupon the structure of the fusion device to be implanted.

An alternative embodiment of the implant driver is shown in FIG. 5. Thedriver 90 includes a shaft 91, having a length sufficient to reach intothe intradiscal space from outside the patient. Connected to the end ofshaft 91 is a head which defines a pair of opposite tongs 93, each ofwhich are configured for flush contact with the flat truncated sidewalls 22 of the fusion device 10. Like the tongs 54 of the previouslydescribed implant driver 50, the outer surface of the tongs iscylindrical to correspond to the cylindrical threaded portion of thedevice.

Unlike the implant driver 50, the driver 90 of the embodiment in FIG. 5uses an expanding collet assembly to firmly grip the fusion device 10for insertion into the body. Specifically, the head 92 adefines a collet94 having a central collet bore 95 formed therethrough. The collet 94terminates in an annular flange 96 that at least initially has adiameter slightly smaller than the inner diameter of the fusion device10 at its end 12. An expander shaft 97 slidably extends through thecollet bore and includes a flared tip 98 situated adjacent and extendingjust beyond the annular flange 96. The flared tip 98 of the expandershaft 97 starts at a diameter sized to slide within the collet bore 95and gradually flares to a diameter larger than the bore.

The implant driver 90 further includes a puller shaft 99 slidablydisposed within a bore 100 defined in the shaft 91. The puller shaft 99has a locking chamber 101 at its end which engages a locking hub 102formed at the end of the expander shaft 97. The puller shaft 99 projectsbeyond the end of the shaft 91 for access by the surgeon. When thepuller shaft 99 is pulled, it pulls the expander shaft 97 away from theannular flange 96 of the collet 94 so that the flared tip 98 becomesprogressively engaged within the collet bore 95. As the tip 98 advancesfurther into the bore 95, the annular flange 96 expands from its initialdiameter to a larger second diameter sufficient for firm grippingcontact with the interior of the fusion device 10. With the fusiondevice so engaged, the implant driver can be used to insert the device10 into the surgical site, after which the expander shaft can beadvanced beyond the collet bore to release the flat tip and,consequently, the fusion device.

In certain circumstances, it may be necessary to drive the fusion device10 deeper into the disc space. When either of the implant drivers 50 or90 is engaged to the fusion device, the device can be readily advancedfarther into the disc space. However, once the implant driver is removedand it is then discovered that the fusion device needs to berepositioned, the flexible nature of the tongs 54 and 93 of the twoimplant drivers makes reacquisition of the now implanted fusion devicedifficult. To alleviate this difficulty, a driving tool attachment 120is provided, as shown in FIG. 6. The driving tool attachment 120includes a body 121 having a first end 122 and an opposite second end123. Like the fusion implant, the body 121 of the driving toolattachment 120 includes a cylindrical portion 125 and opposite flat sideportions 126. The opposite side portions 126 are configured to beengaged by the tongs of the above driving tools 50 or 90.

The driving tool attachment 120 includes a pair of opposing flanges 130at end 123. The flanges 130 are configured to engage the opposite flatsurface 122 on the fusion implant 10, in a manner similar to thataccomplished by the tongs of the implant driver 50 and 90. The end 123also includes a boss 131 which is configured to be inserted into theopening at the end of the implant 10 (see FIG. 7). In use, the drivingtool attachment 120 can be engaged with one of the driving tools 50 or90, with the tongs firmly grasping the flat surfaces 126, as shown inFIG. 7. The driving tool attachment can then be advanced into the discspace with the flanges 130 oriented across the space so that they canreadily interface with the flat surfaces 22 of the fusion device 10.When the driving tool attachment 120 is properly aligned, the boss 131projects into the hollow opening 15 at the anterior end 12 of the fusiondevice and the flanges 130 engage the opposite flat surfaces 22 of thedevice. The driving tool can then be rotated as if the fusion implantwere directly engaged to the main driving tool. The attachment readilytransmits the rotational driving force to the implant 10 to thread itdeeper into the disc space or to retract it back within the disc space.One particular advantage provided by the driving tool attachment 120 isthat the relatively flexible tongs of the two driving tools 50 and 90can be already engaged to the attachment 120 before insertion into thesurgical site. This eliminates a great deal of fiddle factor and avoidsthe risk that the tongs would be unable to firmly grasp the implant 10when it is already in position within the disc space.

In a further embodiment of the present invention, an interbody fusiondevice is provided that permits supplemental fastening to the adjacentvertebrae. In particular, an interbody fusion device 250, as depicted inFIG. 8, includes a hollow body 251 having a first end 252 and a secondend 253. The hollow body 251 defines a hollow interior 255 and includesan end wall 256 at the first end 252. Like the fusion device 10 shown inFIG. 1, the interbody fusion device 250 includes external threads 258spanning a substantial portion of the length of the hollow body 251, anda continuous thread 259 adjacent the second end 253 of the body. Alsolike the fusion device 10, the interbody fusion device 250 includesopposite flat sidewalls 262 that interrupt the external threads 258, aswell as opposing slots 263 offset from the flat sidewalls 262 which alsointerrupts a portion of the external threads 258. Thus far, theinterbody fusion device 250 is substantially similar to the device 10shown in FIG. 1. For example, the device can be tapered so that it has alarger diameter at the first end 252 than at the second end 253. Inaddition, side windows 264 (see FIG. 10) can be provided in the flatsidewalls 262. The side walls 262 essentially divide the body 251 intoupper and lower threaded portions that are configured to be threadedlydriven into adjacent vertebrae.

In accordance with this embodiment, the interbody fusion device 250includes a pair of driver openings 265 defined in the end wall 256 atthe first end 252. Intermediate between the driver openings 265 are apair of offset screw bores 267. In this preferred embodiment, the screwbores 267 are formed so that their respective longitudinal axesintersect and project out from the top and bottom portions 260, 261.Preferably the axes are arranged to intersect the slots 263 in the topand bottom of the fusion device. In this configuration, the longitudinalaxes of the two screw bores intersect outside the hollow body 251 andthe end wall 256, as seen in FIG. 10. A threaded bore 270 is formedbetween the two screw bores 267. The screw bores 267 also define arecessed portion 268, while the threaded bore defines a recessed portion271 that intersects each of the recessed portions 268 of the screw bores267 at an overlap 272.

In using the interbody fusion device 250, a driving tool attachment 275is provided that permits insertion of the device within a properlyprepared intervertebral space. As depicted in FIG. 9, the driving toolattachment 275 is similar to the implant driver shown in FIG. 6. In thisinstance, the driving tool attachment 275 includes a body 276 havingopposite flat sidewalls 277, so that the body is adapted to be engagedby the implant driver 90 in the manner depicted in FIG. 7. In accordancewith the present embodiment, the driving tool attachment 275 includes apair of spaced-apart driving bosses 278 projecting from a mating face279. The bosses 278 are sized and shaped to fit within the driveropenings 265 when the mating face 279 is in direct contact with the endwall 256 of the fusion device 250. The driving tool attachment 275 canbe engaged to a fusion device, such as device 250, to permit threadingof the device into the intervertebral disc space, such as the spacebetween lumbar vertebrae L4 and L5, as shown in FIG. 10.

With the fusion device 250 appropriate positioned within theintervertebral disc space, a pair of bone screws 280 can be extendedthrough respective screw bores 267 in the hollow body 251. The screwsare passed through the bores 267 until the bone engaging threads of thescrews 280 contact the vertebral bone. As the bone screws 280 arethreaded into the vertebral bone, the head 281 of each of the bonescrews 280 seats within the respective recessed portions 268 of each ofthe screw bores 267. In this orientation, the heads 281 of the bonescrews 280 are flush with or below the surface of the end wall 256 ofthe fusion device 250. At this point, a locking screw 282 can bethreaded into the threaded bore 270. As the locking screw is tightenedinto the bore 270, the head 283 of the locking screw contacts the heads281 of both bone screws 280. Further tightening of the locking screw 282causes the head 283 to seat within the recessed portion 271 to trap theheads 281 of the bone screws 280 within their respective screw bores267. Thus, the set screw 282 prevents backout of the bone screws 280when they are engaged within the adjacent vertebrae.

The diverging bone screws 280 provide greater stability to the fusiondevice 250 than can be achieved with prior threaded devices. The bonescrews enhance the resistance to retrograde expulsion of the device andprevents counter-rotation or unthreading. The bone screws 280 can be ofa wide range of sized provided that the screws are long enough toachieve an effective purchase in the adjacent vertebrae.

In accordance with additional aspects of the present invention, twomethods for implanting an interbody fusion device, such as the devices10 or 250, are contemplated. First, with reference to FIGS. 11(a)-11(d),an anterior approach is shown. As a preliminary step, it is necessary tolocate appropriate starting points for implanting the fusion device,preferably bilaterally. In the first step of the anterior approach, adistractor 75 is disposed between the vertebral end plates E to dilatethe L4-L5 or L5-S1 disc space. (It is understood, of course, that thisprocedure can be applied at other vertebral levels). In the second step,shown in FIG. 11(b), an outer sleeve 76 is disposed about the discspace. The outer sleeve 76 can be configured to positively engage theanterior aspect of the vertebral bodies to firmly, but temporarily,anchor the outer sleeve 76 in position. In essence, this outer sleeve 76operates as a working channel for this approach. In the step of FIG.11(b), a drill 77 of know design is extended through the outer sleeveand used to drill out circular openings in the adjacent vertebralbodies. The openings can be tapped to facilitate screw insertion of thefusion device 10, although this step is not necessary.

In the next step shown in FIG. 11(c), the fusion device 10 is engaged bythe implant driver 50 and extended through the outer sleeve 76 until thestarter thread 19 contacts the bone opening. The implant driver 50 canthen be used to screw thread the fusion device into the tapped oruntapped opening formed in the vertebral end plate E. It is understoodthat in this step, other suitable driving tools could be used, such as ascrew driver configured to engage the driving tool slots 29 at theanterior end 12 of the device 10. The degree of insertion of the fusiondevice 10 determines the amount of lordosis added or restored to thevertebral level. In the final step, the implant driver is removedleaving the fusion device 10 in position. It can be seen that onceimplanted, the closed posterior end 13 is directed toward the posterioraspect of the vertebrae. The hollow interior 15 is open at its anteriorend 12, but can be closed by a plastic or metal material, if necessary.

In a second inventive method, as depicted in FIGS. 12(a)-12(d), aposterior approach is implemented. The first two steps of the posteriorapproach are similar to that of the prior anterior approach, except thatthe distractor 75, outer sleeve 76 and drill 77 are introducedposteriorly at the instrumented motion segment. This approach mayrequire decortication and removal of vertebral bone to accept the outersleeve 76. In the third step of this method, the fusion device 10 isinserted through the outer sleeve 76 into the dilated disc space. It isunderstood that the disc space is preferably dilated only to the extentnecessary to receive the implant with the truncated side walls 22directly facing the vertebral end plates E. Thus, as shown in FIG.12(c), the bone ingrowth slot 27 is facing laterally, rather thancoronally, as expected for its final implanted position. A suitabledriving tool 80 can be provided to project the fusion device 10 throughthe outer sleeve 76 and into the intradiscal space. In one embodiment,the driving tool 80 includes a projection 81 which is configured toengage a slot opening formed in the end wall at the posterior end 13 ofthe fusion device 10. An internal thread (not shown) can be used to fixthe device 10 to the driver 80.

Once the fusion device 10 has been advanced into the intradiscal spaceto the appropriate depth relative to the pivot axis P of the vertebrae,the driving tool 80 is used to rotate the implant in the direction ofthe rotational arrow R in FIG. 12(c). As the driving tool 80 is rotated,the device itself rotates so that the interrupted threads 18 startcutting into the vertebral bone at the end plates E. In this manner, theimplant operates as a cam to separate the adjacent vertebrae in thedirection of the spreading direction arrows S in FIG. 12(c). Thiscamming approach provides a somewhat easier insertion procedure than forthe anterior approach of FIGS. 11(a)-(d) in that a single rotation isrequired to lock the implant into the vertebral bone. In contrast, theformerly discussed screw insertion technique of the anterior approachrequires continuous threading of the device into position.

With either the anterior (FIGS. 11(a)-(d)) or the posterior approach(FIGS. 12(a)-(d)), the position of the fusion device 10 with respect tothe adjacent vertebrae can be verified by radiograph or other suitabletechniques for establishing the angular relationship between thevertebrae. Alternatively, the preferred depth of insertion of theimplant can be determined in advance and measured from outside thepatient as the implant is positioned between the vertebrae. The depth ofinsertion of the fusion device can be ascertained using depth markings(not shown) on the implant drivers 50, 90 or 80.

In another embodiment of the inventive surgical technique, laparoscopictechnology is used to provide a sealed and protected channel forinstruments and implants directed to the subject disc space. Inaccordance with one aspect of this inventive method, an anteriorapproach to the L5-S 1 motion segment is illustrated. It is of courseunderstood that these same techniques and instruments to be describedbelow could be used at different vertebral levels or in a posteriorapproach under appropriate conditions.

As depicted in FIG. 13, the present inventive technique includes makinga small incision 140 and preferably inserting an insufflator needle intothe abdominal cavity. Fluid is introduced into the abdominal cavitythrough the insufflator needle to a pressure of preferably approximately1 Smm of mercury to assist in visualization of the surgical site. Aninitial port 141 for the laparoscope is placed five to ten centimeterscephalad of the umbilicus in the midline ten millimeters in length. Theabdomen is visually explored and the patient is placed in steepTrandelenburg. The abdominal wall is visualized endoscopically as twoworking ports 142, 143 are placed just lateral to the epigastricvessels, opposite the level or levels to be fused. It is believed to beadvantageous to stagger the ports slightly from direct opposition toeach other.

The preferred method continues with insertion of retractors through theports 142, 143. The retractors can be used to sweep the small bowelsuperiorly out of the pelvis. The sigmoid colon is also pulled out ofthe pelvis and held laterally with the left fan retractor. For fusion atthe L5-S1 junction, the sacral promontory and drop-off can be easilyseen at this point. The posterior peritoneum overlying the L5-S1 discspace is then incised longitudinally with endoshears for the desiredexposure. Using opposing fan retractors as blunt dissectors, the softtissue underlying the parietal peritoneum can be swept laterally tobilaterally expose the anterior L5-S2 disc annulus. The sacral arteryand vein coursing the disc are individually ligated with hemoclips andtransected. A dissector can be used to remove residual soft tissue overthe disc. Exposure is maintained with the left fan retractor in placeholding the colon out of the way. It has been found that usually theright side does not require retraction, so a suction irrigation cathetercan be used through this port.

In one specific procedure for the L4-L5 disc, the posterior peritoneumis incised more proximally about 3 centimeters. Again, the left fan isused to retract the colon laterally and with careful blunt dissectionthe aorta is exposed anteriorly at the bifurcation. The L4-L5 disc isusually right below this point. Left lateral dissection is carried outover the left common iliac vein and artery, gently retracting thesevessels to the right. In order to retract these vessels enough to theright for adequate disc exposure the ascending segmental vein branchmust be identified and transected. Once this vessel is cut, the arteryand vein can then be bluntly retracted to the right with a fan or loopretractor to expose a significant amount of the L4-L5 disc for fusion.

Once the subject disc is exposed, it can be important to align theabdominal entry operating trocar port site 145 with the disc to be fusedso that the operating trocar is parallel with the endplates of the discin the sagittal plane. The entry point is estimated and a smallSteinmann pin can be placed either in the interspace or along thepatient and checked with lateral C-arm and adjusted accordingly. A 1.5to 2.5 centimeter incision can be made for placement of the operatingtrocar. A blunt introducer is placed in the abdomen and an 18 mm workingtrocar 147 (FIG. 14) can be placed over it under endoscopicvisualization.

In accordance with a further aspect of the present embodiment of thesurgical technique, the annular of the subject disc D is marked forbilateral placement of a pair of fusion devices. For example, as shownin FIG. 14, a working trocar 147 is situated within the working port 145(see FIG. 13). The bilateral marks can be made with a template 150, asshown in general in FIG. 14 and in more detail in FIG. 15. Greaterdetail concerning this template and its method of use can be found inU.S. Pat. No. 5,645,549, issued on Jul. 8, 1997. The description of thistemplate in this co-pending application is incorporated herein byreference.

For convenience, a brief description of the template will be made withspecific reference to FIG. 15. In particular, the template 150 includestubular body 151 and an elongated guide foot 152 that is pivotableconnected to the end 153 of the tubular body. A guide wire or stylet 155extends through the tubular body to pivot the foot 152 to the side. Thesharp tip 156 of the stylet can then be used to pierce the disc annulusD. Using a mallet, the template can be secured to the center of the discspace by driving the stylet 156 into the disc tangential to thecurvature of the annulus and parallel to the endplates. The template canthen be slide down the guide wire or stylet until the foot 152 contactsthe disc annulus.

The foot includes an opening 157 through which an electrocautery device160 can extend. The tip 161 of the electrocautery device is guidedthrough the opening 157 in the foot 152 to contact the disc annulus D.When the tip 161 is energized, it leaves a mark MR that is lateral tothe center of the subject disc. The template 150 can then be rotated inthe direction of the arrow T so that the foot is situated laterallyopposite the first mark MR. At that point, the electrocautery device canbe used to make a second mark ML providing the bilateral positions forthe two fusion devices.

Once the bilateral marks MR, ML have been made on the disc annulus, thesurgeon has a visual indication as to the proper location for placementof the fusion device. Under direct visualization of the insufflatedabdominal region by way of a laparoscope through port 141 (FIG. 13), thesurgeon can then direct a T-handle probe 160 through the working port147 to the either of the cauterization marks MR and ML (FIG. 16). TheT-handle probe 160 includes a sharp tip 161 that is used to breakthrough the disc annulus. The T-handle allows the surgeon to rotate theprobe 160 as necessary to facilitate penetration into the annulus. Oncean initial opening has been made in the disc annulus by way of theThandle probe 160, a T-handle trephine 165 can be used to create pilotholes for subsequent instrumentation. The T-handle trephine 165 caninclude a series of marking 166 at 5 mm increments to control the depthof insertion of the trephine into the disc space, as shown in FIG. 17.The markings 166 are compared to the working trocar 147 to gauge thedepth of the cutting edge of the trephine, and therefore the depth ofthe prepared bore in the disc space and vertebral endplates. Again, theT-handle of the trephine allows the surgeon to rotate the trephine 165.This procedure is repeated at both of the electrocautery marks ML andMR. At this point, the surgeon has two bilateral holes to use fororientation during the remainder of the procedure. The trephine 165 isalso preferably used to core into the disc space to form bilateralbores. A rongeur may be used to clear disc material from each of thebilateral bores in the disc.

In accordance with further steps of the present inventive method, adistractor 167 is advanced through the working trocar 147 as shown inFIG. 18. The distractor has a distractor tip 169 that is selectedaccording to the vertebral level being instrumented. For instance,distractors for a 16 mm size implant can be either 12 mm or 14 mm inwidth to maintain the disc space at its proper anatomical height. Thetip 169 is removably attached to a distractor shaft 168. Preferably,progressively larger distractor tips are sequentially inserted inalternating fashion into each of the bilateral holes in the disc spaceand annulus until the annulus is taut and the adjacent vertebrae areadequately distracted for restoration of a proper disc space height. Inone aspect of the invention, the distractor tips 169, once they aredisposed in their bilateral positions, will acts as a centering point oralignment guide for use of the instruments throughout the remainder ofthe procedure. It is therefore important that the distractor tips 169 beproperly located, which can be accurately confirmed with fluoroscopy.

Once the bilateral distractor tips have been properly seated, a shaftextension (not shown) can be engaged to distractor shaft 168. At thispoint, in accordance with the preferred embodiment, the disposabletrocar 147 is removed and a laparoscope 170 is introduced through theport 145 in the skin and into the disc space, using the distractor shaftand distractor tip as a positioning guide. In accordance with oneembodiment of the present invention, the laparoscope 170 includes anouter sleeve 171 having a first end 172 and a second end 173, as shownin FIG. 19. The second end 173 is engaged to a laparoscopic port 180which can be of conventional design. In particular, the laparoscopicport 180 can include a bore 184 (FIG. 20(a)) extending therethrough andin communication with the interior of the hollow outer sleeve 171. Thisbore 184 in the laparoscopic port allows introduction of instrumentsthrough the port and into the outer sleeve 171. The bore is preferablyclosed by a number of seals 182, which are configured to acceptcylindrical tools and instruments therethrough while maintaining tightsealed engagement about the instrument.

The laparoscopic port 180 also preferably includes a trumpet valve 183,which can be of conventional design. Specifically, the trumpet valve 183maintains the laparoscopic port 180 in a normally closed position inwhich its internal bore is closed from communication with the outersleeve 171. However, once a instrument is introduced into the port 180through the seals 182, the trumpet valve 183 moves aside to allowpassage of the instrument or tool into the sleeve 171.

In a further unique aspect of the invention, the end 172 of the outersleeve 171 includes a pair of opposite distraction extensions or fingers173. These distraction fingers 173 are sized according to the height ofthe particular disc space. Specifically, the fingers 173 are intended tomaintain the spacing between the adjacent vertebrae during subsequentsteps of the procedure after the distractor tip 169 has been removed.Thus, the width of the fingers 173 can be varied depending upon theparticular vertebral level being instrumented. In addition, thedistraction fingers 173 can be tapered to conform to a normal anglebetween adjacent vertebrae at the instrumented level. The position ofthe fingers 713 is correlated with the position of the distractor tipswithin the bilateral bores in the disc space by aligning the fingers 173with the trumpet valve 183 when the port 180 is engaged to the outersleeve 171. When the laparoscope 170 is inserted, the trumpet valvesprovide a visual indication of the alignment of the fingers. In otherwords, when the trumpet valve 183 is lateral to the midline, the fingers173 are properly oriented between the vertebral endplates.

In one specific embodiment, the outer sleeve 171 can include oppositespikes 174 disposed between the distraction fingers 173. These spikesare preferably configured to penetrate at least partially into theadjacent vertebral bodies, to help maintain the position of the outersleeve 171 at the surgical site. In some instances, the outer sleeve 171does not include the teeth 174. For example, where the procedure is toimplant a tapered fusion device, the teeth 174 are preferably eliminatedand where the device is a uniform cylinder, the teeth can be retained.

In one embodiment of the present surgical method, the laparoscope 170can be directly inserted over the distractor shaft extension (notshown). However, it is believed that the distraction fingers 173 and thespikes 172 can cause trauma to the skin during entry and to the softtissue surrounding the surgical site during introduction of thelaparoscope 170. Thus, a further feature of the preferred embodimentincludes a switching sleeve 190, as shown in FIGS. 20(a), (b). Theswitching sleeve 190 has a length sufficient to span the entire lengthof the laparoscope 170 from the port seals 182 to the end 172 of theouter sleeve 171. In particular, the switching sleeve 190 has a taperedtip 191 configured to extend beyond the end 172 of the outer sleeve 171,and more particularly beyond the ends of the fingers 173. The switchingsleeve 190 also includes a flared tip 192 at its opposite end that isenlarged to prevent its passage through the laparoscopic port 180 andparticularly the seals 182. In accordance with a preferred embodiment ofthe inventive surgical procedure, the switching sleeve 190 is placedinside the laparoscope 170 prior to insertion into the patient. Theswitching sleeve 190 has an outer diameter nearly equal to the innerdiameter of the outer sleeve 171 to slide in close running fit withinthe laparoscope 170. The laparoscope 170 and switching sleeve 190 canthen be slide over the distractor shaft and with a twisting motion passthrough the skin and fascia until the outer sleeve contacts the discannulus. It is important to consider that the opposite fingers 173 onthe outer sleeve 171 of the laparoscope must pass through the opening inthe disc space and be aligned between the adjacent vertebrae. As thefingers 173 are pushed into the disc space, the switching sleeve 190will remain outside the disc annulus as its tapered tip 191 contacts theannulus in the region between the distraction fingers 173 (see FIG.20(b)). The outer sleeve 171 of the laparoscope 170 is properly orientedwhen the fingers 173 are correctly oriented between and contacting theadjacent vertebra endplates. The outer sleeve 171 is then seated bystriking a driving cap (not shown) mounted on the laparoscopic port, tothereby drive the fingers 173 fully into the disc space between thevertebral endplates and to drive the spikes 174 into the adjacentvertebrae.

With the laparoscope 170 in place, all of the remaining steps of thisinventive technique occur under a relatively protected or sealedenvironment. Specifically, the outer sleeve 171 of the laparoscopeprovides a sealed passageway from the bilateral bores at locations MRand ML on the disc to the laparoscopic port 180 outside the patient. Thelaparoscope 170 can be used as a passageway to provide irrigation andaspiration where necessary, without the risk of fluids leaking into thespace adjacent the operative site. Moreover, the sealed working channelto the prepared sites in the disc space prevent leakage of abdominaldistension fluids into the working channel and disc space. This latteraspect allows direct vision of the surgical site outside the workingchannel created by the laparoscope.

With the laparoscope 170 in position, the distractor shaft 168 isremoved as well as the distractor tip 169 that is disposed between theadjacent vertebrae. Since the fingers 173 of the laparoscope outersleeve 171 will maintain the spacing between the adjacent vertebrae, thedistractor tip is being removed from the disc space to preventdislodgment of the outer sleeve. In a bilateral procedure, the bilateralbores in the disc each contain a distractor tip. In the preferredmethod, the right left bore remains in place. Thus, the fingers 173 ofthe laparoscope engaged within one of the bilateral locations share thedistraction load with a distractor tip 169 disposed within the otherbilateral location. When the right side is instrumented with a fusiondevice, as described below, the fingers 173 will be within the left borein the disc and will share the distraction load with the fusion device.

With the distraction tip removed and the disc space supported by thefingers 173, the next step in the inventive method is the preparation ofthe vertebral end plates and disc to provide a site for insertion of afusion device. The switching sleeve 190 is first removed and, inaccordance with one aspect of the invention, a reaming sleeve 195 isadvanced through the laparoscope 170. As shown in FIG. 21, the reamingsleeve 195 includes spikes 196 that are adapted to penetrate theadjacent vertebral bodies to hold the reaming sleeve in place. Oneobject of the reaming sleeve in this embodiment is to help maintain theposition of the laparoscope while the disc material and vertebral endplates are being reamed. This object is of particular importance whenthe laparoscope outer sleeve 171 does not include the teeth 174. Inaddition, the spikes 195 on the reaming sleeve 195 will prevent thevertebral bodies from being pushed away or distracted while reaming,since the force generated by the reamer can have a tendency to drive thevertebral bodies apart. This force is particularly present when atapered fusion device is to be implanted, necessitating cutting conicalthreads into the vertebra.

In accordance with the invention, an adjustable reamer 197 is extendedthrough the reaming sleeve 195. The reamer 197 can be of conventionaldesign with a cutting surface configured to evacuate the disc space andprepare the adjacent vertebral bodies to receive a threaded implant. Thereamer 197 includes an adjustable depth stop 198 disposed adjacent thelaparoscopic port 180. The depth stop 198 contacts the seals 182 of theport to prevent introduction of the reamer 197 to deeply into the discspace. The depth of reaming necessary, and consequently the position ofthe depth stop 198, can be determined prior to this reaming step byreview of fluoroscopic images.

The reamer 197 is manually operated by way of a T-handle 199 tosuccessively remove disc tissue and bone from the adjacent vertebralbodies to provide a prepared bore for the fusion implant. Preferably,several passes will be made with the reamer, after which the outersleeve will be examined visually and fluoroscopically to verify that itremains fully seated within the disc space. In addition, the reamingshould be observed under C-arm imaging to prevent reaming into thespinal canal. Preferably, the depth stop 198 will be set at an initialdrilling depth less than the anticipated full depth for implantinsertion. For example, for an L5-S1 fusion, a 20 mm deep reamed boremay be prepared for a 26 mm long implant.

After the disc material and vertebral bodies have been reamed by thereamer 197, one prepared site is available for insertion of the fusionimplant at the right location MR. It is then necessary to prepare theother bilateral location previously marked using the template 150(location ML in FIG. 15). In the next steps of the inventive method, thereamer 197 is withdrawn as well as the reaming sleeve 195. Thelaparoscope 170 is then unseated in a controlled manner so that thefingers 174 are disengaged from between the vertebrae and withdrawnthrough the opening of the disc annulus. However, the laparoscope 170,and particularly the outer sleeve 171, is not removed from the skinafter unseating from the disc space. Instead, the outer sleeve isreoriented over the second bilateral location ML (see FIG. 15).Preferably, immediately after the outer sleeve 171 is disengaged fromthe disc annulus, the switching sleeve 190 is extended back through theouter sleeve 171 so that the tapered end 191 of the sleeve extendsbeyond the fingers 173. The switching sleeve will then protect the softtissue surrounding the instrumented disc space as the outer sleeve 171is repositioned over the second bilateral location ML.

With the laparoscope 170 oriented over the second location ML and withthe switching sleeve 190 contacting the disc annulus, a distractor tip169 attached to a distractor shaft 168 is extended through the outersleeve 171. In the preferred technique, the laparoscope is not yet fullyseated at this location ML. The distractor tip 169 is advanced throughthe bore within the disc and anchored between the adjacent vertebral endplates. The laparoscope 170, and particularly the outer sleeve 171, isreseated within the disc space in the manner described above, namelywith the distraction fingers 173 disposed between the vertebral endplates. Once the position of the outer sleeve and fingers 173 isconfirmed using fluoroscopy, the remaining steps for preparing thevertebral bodies to receive the fusion implant are repeated at the leftlocation ML.

Once the second bore in the disc space has been prepared, the followingsteps of the technique involve insertion of the implant. In accordancewith the present invention, the implant can be a fision cage of the typeshown in FIG. 1 which is tapered to restore the normal curvature at theparticular vertebral level. In the case of a fusion cage of the typeshown in FIG. 1, the implant driver 50 can be used to implant the device10. The implant drive 50 can be substantially as depicted in FIG. 2 andcan engage the implant 10 as shown in FIG. 3. In accordance with thepresent technique, the implant drive 50 can be engaged by a T-handleassembly 200, as shown in FIG. 22. The T-handle assembly 200 includes acollet 201 which engages the end of the implant drive 50 opposite thegripping tongs 54. The assembly 200 also includes T-handle 202 which isaligned with the gripping tongs 54 so that the surgeon has a visualindication of the orientation of the tongs 54 when the implant driver560 is extended through the laparoscope 170.

In accordance with the preferred technique, the implant drive 50carrying the fusion device 10 is inserted through the laparoscopic port180 and through the outer sleeve 171 until the implant 10 contacts theprepared bore within the disc space. At that point, the implant drive 50can be rotated using the T-handle 202 to thread the implant into theprepared bore. The implant driver 50 can preferably include a pluralityof depth markings on the driver shaft 51 beneath the collet 201 to givethe surgeon the visual indication of the depth of insertion of theimplant 10 into the prepared bore. Once the implant has been screwed into its predetermined depth, as indicated by the depth markings on theimplant drive shaft 51, insertion of the implant should be halted withthe T-handle 202 parallel to the vertebral end plates. With thisorientation of the T-handle 202, the tongs 54 of the implant drive 50will be exposed to the disc space, rather than in contact with thevertebral bone. Consequently, then the long slots 27 (see FIG. 1) of thefusion device 10 will be directly exposed to and in contact with thevertebral bodies.

With a fusion device 10 implanted within the left location ML, theimplant driver is removed from the implant and the laparoscope 170 isunseated from the left bilateral location. Again, the laparoscope 170 isnot removed from the skin after unseating, but is simply moved to thenext bilateral location MR, preferably with the switching sleeve 190protecting the surrounding tissue from the distraction fingers 173 ofthe laparoscope. At this location, the same steps are repeated toimplant a second fusion device 10 at this right location.

When each of the implant devices 10 is bilaterally implanted within thedisc space, the position of the implants should be confirmed. In someinstances, it may be necessary to reposition an implant within the discspace, such as by driving it further into the disc space. In thisinstance, the driving attachment 120 can be engaged to the implant drive50 and the attachment 120 engaged with the implanted device 10 to permitadditional manipulation of the device.

In switching between the left location RL and the right location MR, itis preferred that the implant drive 50 be fully removed from thelaparoscope 170 and the switching sleeve 190 extended through the outersleeve 171. Also, the distractor tip 169 attached to the distractorshaft 168 should then be extended through the switching sleeve 170 andthe distractor tip can be used to locate the previous bore at the rightlocation MR. Once the distractor tip 169 is situated within the bore,the outer sleeve 171 can be seated at the right most location in thedisc space. With the outer sleeve 171 properly seated, the distractorshaft can be removed to make way for the implant drive 50 carrying a newimplant fusion device 10. Of course, the switching sleeve is removedprior to extending the implant and implant drive through the outersleeve 171.

Once both fusion devices are disposed in their bilateral positions atlocation ML and MR, an A-P radiograph can be taken to assure properplacement. In addition, where possible, it is preferred that additionalbone graft material is packed around the implants in situ to furtherfacilitate fusion.

As discussed above, the fusion device 10 includes a hollow opening 15 toreceive bone growth material. In one specific embodiment, this bonegrowth material can include autogenous bone harvested from the patient'santerior iliac crest. Autograft bone from other locations, autologousbone, allograft, bone growth substitutes or other bone material capableof promoting or inducing bone ingrowth can be loaded into the implant.In the preferred technique, the interior 15 of each fusion implant 10 isfilled prior to insertion of the implant into the disc space.

The facilitate this “pre-loading” of the fusion material, an implantholder 210 is provided in accordance with the invention (FIG. 23). Thisholder 210 includes a base 211 that includes a fixed clamp section 212and a movable clamp section 215. The fixed clamp section 212 includes aflange 213 projecting from the base 211. The movable clamp sectionincludes an impactor plate 216 that slides within a groove 217 formed inthe base 211. The impactor plate 216 is connected by a threaded shaft218 to a knob 219. The threaded shaft is rotationally supported by anupstanding flange 221 attached to base 211. The upstanding flange 221includes a threaded bore (not shown) through which the threaded shaft218 extends. As the knob 219 is rotated, the shaft rotates within thethreaded bore of the flange 221 to move the impactor plate 216 forwardtoward the fixed clamp half 212.

In accordance with the present embodiment, a pair of blocks 225 and 226are provided which are disposed adjacent a corresponding one of clampsections 212 and 215. The blocks 225 and 227 include implant engagementsurfaces 226 and 228 which are configured to match the outer shape ofthe implant at its large slots 27. These blocks, therefore, serve toclose off the slots 27 as bone growth material is packed into theopening 15 of the implant 10. In one specific embodiment, the blocks 225and 227 are formed of plastic to effectively seal the large openings 27in the sides of the implant 10. Once the bone growth material has beentightly compacted within the implant device 10, the knob 219 can berotated in the opposite direction to release the movable clamp 216 fromthe device 10.

In accordance with another aspect of the present invention, thelaparoscope 170 can be used to implant a bone dowel 240, as depicted inFIG. 24. The bone dowel 240 can be of a variety of configurations, suchas an allograft Crock dowel, autograft tricortical or button dowels,manufactured composite dowels or hybrid dowels (e.g., an autogeneousbutton combined with allograft Crock dowel). While it is preferable thatthe bone dowel 240 be cylindrical, this configuration is not essentialto the invention, provided the dowel is configured to pass easilythrough the outer sleeve 171 of the laparoscope.

In accordance with this embodiments, the disc space and adjacentvertebral bodies are prepared as described above (see, FIGS. 13-21 andaccompanying text). In the preferred technique for implanting a bonedowel, the reamer 197 is used to create a partially cylindrical cut inthe vertebral endplates to receive a cylindrical dowel. Alternatively,if a non-cylindrical dowel is used, the endplates can be preparedaccordingly. It is understood that the dowel will typically have auniform outer diameter or width corresponding to the disc space height.Unlike the fusion device 10 discussed above the bone dowel is nottapered; however, preparation of the vertebral bodies with the tapereddistraction fingers 173 of the outer sleeve 171 providing an appropriateangle will allow the implanted bone dowel to retain this angle.

Once the disc space and vertebral endplates have been prepared toreceive the dowel, the bone dowel 240 is dropped into the laparoscopethrough outer sleeve 171. Due to the precise fit between the bone doweland the vertebral endplates, resistance will be experienced duringinsertion of the dowel. An impactor 245 is provided to drive the dowelinto its prepared site. The impactor includes an impactor head 246 thatis preferably threaded engaged to an impactor shaft 247. The head andshaft are sized for a close running fit through the outer sleeve 171.Preferably, the impactor head 246 can be provided to be implanted. Alsopreferably, the impactor shaft 247 will have a smaller diameter so thatit can be used with impactor heads and outer sleeves of severaldiameters.

The impactor shaft 247 includes a driving cap 248 that can be strickenby a hammer or similar tool to drive the bone dowel into the preparedsite in a controlled manner. Preferably, the impactor shaft alsoincludes a series of depth markings 249 corresponding to the depth ofinsertion of the bone dowel 240 into the disc space. The final positionof the dowel can be verified later by A-P radiograph. The second bonedowel can be inserted in a similar manner and additional bone graftplaced between the bilateral bone dowels.

The present invention involves instruments and surgical techniquesusable at any level of the spine. For simplicity, the above discussionhas focused on fusion of the L5-S1 disc space. The dimensions of each ofthe components of the instruments would be sized appropriately for thespecific vertebral level being instrumented. For example, the fusiondevices 10 may be offered in several sizes, including 12 mm, 14 mm, and16 mm. Based upon the size of the fusion implant, the trephine 165 canbe provided in several sizes, such as trephines to form bores having adiameter of 6 mm, 8 mm or 10 mm.

The distractor tips 169 are also sized according to the size of thefusion device to be implanted. Preferably, the distractors are smallerthan the fusion device. For example, for a 16 mm fusion device, thedistractor tips 169 can be either 12 mm or 14 mm. For a 16 mm fusiondevice, a 16 mm reaming sleeve is provided to accept a 16 mm reamer toprepare a hole of the same diameter within the disc space and vertebralbodies. Smaller reamers and reaming sleeves would be provided forsmaller fusion devices. As previously described, the outer sleeve 171 ofthe laparoscope 170 is preferably a 2 mm in diameter to readily acceptall of the instruments and sleeves passing therethrough during theseveral steps of the inventive procedure.

In the surgical techniques described above in relation to FIGS. 13-21,an outer sleeve 171 is utilized which incorporated fingers 173 thatserved to maintain distraction of the intervertebral space. In addition,the prior illustrated technique utilizes a series of distractor tips 169that are used to maintain distraction at one side of the disc spacewhile a fusion device is implanted in the other bilateral location. Afurther embodiment of the present invention provides an improvement tothis technique. Specifically, this improvement resides in a distractionmechanism that is centrally disposed between the bilateral fusion devicelocations. This centralized distraction provides a more uniformdistraction across the entire disc space than can be provided by adistractor tip, such as tip 169, situated at one side or the other ofthe intervertebral space.

In accordance with the embodiment of the invention shown in FIGS. 25-27,a distractor plug 290 is provided that includes an elongated stem 291terminating at one end in a fan-shaped flange 292. The stem is sized tobe maintained within the disc space. In one specific embodiment, thestem 291 has a length of about 22 mm. The flange 292 includes a forwardfacing bone contacting face 293 that is adapted to contact the vertebralbone in a manner disclosed herein. The elongated stem 191 includesopposite inwardly curved or concave walls 194. The curved walls 194 ofthe stem 191 merge into or are contiguous with opposite curved orconcave edges 195 of the flange 192. In accordance with the presentinvention, these curved walls 294 and curved edges 295 are preferablysized to provide clearance for the outer diameter of various tools andinstruments that might be advanced into the intervertebral disc spacethrough an outer sleeve, such as the sleeve 171 described above. In aspecific embodiment, these contiguous curved walls 194 and edges 195 aredefined at a diameter of between 20 mm-29 mm.

The distractor plug 290 further includes a locking surface 297 at thetop and bottom portions of the elongated stem 291 and intermediatebetween the opposite curved walls 294. These locking surfaces 297 canhave a variety of configurations; however, in one specific embodiment,these locking surfaces 297 includes a series of ridges 298 that areadapted to provide a modest grip on the endplates of the adjacentvertebrae that will contact the elongated stem 291 of the distractorplug 290. In accordance with the invention, the elongated stem 291 has aheight between the two locking surfaces 297 that approximates thedistracted height of the disc space to be instrumented. In the case of athreaded fusion device, such as the device 250, this height of theelongated stem 291 will be less than the outer crest diameter of thethreads of the fusion device 250. In a specific embodiment, the top andbottom locking surfaces 297 define an outer diameter of between 10 mm-14mm.

The distractor sleeve 290 further includes a lower stop face 296 that isintegral with the flange 292 but that is on the opposite side of theelongated stem 291 from the bone contacting face 293. The elongated stem291 is hollow with a bore extending along its length, as shown in FIG.26. The stem 291 defines a threaded bore 302 at the end adjacent theflange 292. The threaded bore merges into and communicates with a keyedbore 301 that is at the opposite end of the distractor plug 290. Theopposite end of the stem 291 of the plug 290 forms a blunt nose 299through which the keyed bore 301 exits. In the illustrated embodiment,the keyed bore 301 is square in configuration. Alternatively, the keyedbore can have a variety of shapes that permit a keyed interface with asimilarly shaped spike extending through the bore 301.

In its use, the distractor plug 290 is configured to be pushed into theintervertebral disc space between adjacent vertebrae. The distractorplug 290 is particularly well suited to providing distraction in a discspace spanning a spondylolisthesis condition. In this condition, one ofthe vertebrae is anteriorly offset from an adjacent vertebrae. In thecondition specifically illustrated in FIG. 28, the superior lower lumbarvertebrae L5 is offset from the inferior sacral vertebra S1. Thus, thedistractor plug 290 is advanced anteriorly into the disc space betweenthe lumbar vertebra L5 and sacrum S1.

The blunt nose 299 first contacts the adjacent vertebrae and provides asmooth and steady distraction as the remainder of the plug, namely theelongated stem 291, comes in contact with the endplates of the adjacentvertebrae. In order to drive the distractor plug 290 into this discspace, the present invention contemplates a plug driver 305. While theplug driver 305 can have a variety of configurations, in its simplestform the driver 305 includes a threaded stem 306 projecting from anelongated bar 307. A handle 308 is formed at an opposite end of the bar307 to provide a gripping surface to push the plug driver 305 toward theinstrumented disc space. The threaded stem 306 of the plug driver 305 isconfigured to engage the threaded bore 302 of the distractor plug 290.Thus, the distractor plug 290 is first threaded onto the end of the plugdriver 305 and then subsequently advanced anteriorly into the disc spacebetween the adjacent vertebrae.

As a force F is applied to the distractor plug 290 through the plugdriver 305, the flange 292 is advanced toward the lumbar vertebra L5until the bone contacting face 293 is in contact with the vertebra. Atthis point, further force F applied to the distractor plug 290 not onlypushes the elongated stem 291 into the intervertebral space, but alsopushes the lumbar vertebra L5 into its proper alignment with the sacrumS1.

As the distractor plug 290 is advanced further into the intervertebralspace, the upper and lower locking surfaces 297, and particularly theridges 298, grip the adjacent vertebral endplates to prevent retrogradeexpulsion of the distractor plug 290. The locking surfaces 297 of thedistractor plug 290 provide a sufficiently strong engagement between thevertebral endplates to also prevent restoration of the originalspondylolisthesis condition. The distractor plug 290 is pushed furtherinto the intervertebral space until the stop face 296 of the flange 292contacts the inferior vertebra, in this case the sacrum S1. It isunderstood that this stop face 296 can have a variety of configurationsdepending upon the desired final orientation of the two vertebraerelative to each other. For instance, the flange 292 can be wider at thestop face 296 than at the bone contacting face 292 so that the anteriorportion of the displaced vertebra still retains some anterior offsetfrom the anterior portion of the properly positioned vertebra.

It is known that some threaded cages can permit a reduction of aspondylolisthesis condition, provided the condition is only a grade one.The distractor plug 290, and particularly the locking surface 297 of thestem 291 and the flange 292, permit reduction of higher gradespondylolisthesis conditions. The flange and locking surfaces reduce therisk of slippage between the inferior and superior vertebrae as thesuperior vertebra is reduced.

In an alternative embodiment, a distractor plug 310 is provided thatdoes not include a flange, as in the case of the distractor plug 290shown in FIG. 25. Specifically, the distractor plug 310 shown in FIG. 20includes an opposite curved or concave sidewall 311, a blunt nose 312and opposite locking surface 313. Each of these features issubstantially similar to the features of the distractor plug 290.Likewise, the distractor plug 310 includes a stop face 314 that isadapted to contact the inferior vertebra during the reduction process.Finally, the distractor plug 310 is hollow and includes a threaded bore(not shown) and an integral keyed bore 315.

With this embodiment, the primary reduction force is provided by thedriver 316, depicted in FIG. 30. This driver includes a threaded stem317 that is adapted to engage the threaded bore (not shown) in thedistractor plug 310 of FIG. 29. A driving flange 318 is formed so thatthe threaded stem projects outward from the driving flange 318. Thedriving flange 318 includes a bone contacting surface 319 that at leastinitially contacts only the end of the distractor plug 310 when the stem317 is threaded into the plug. Once the driver 316 is used to push thedistractor plug 310 in place, the bone contacting face 319 abuts thedisplaced vertebra and is used to transmit a force to reduce thatvertebra.

As described above, the distractor plugs 290 and 310 first provide ameans for reducing a spondylolisthesis condition. Once the vertebraloffset has been reduced, the driving tools can be removed and thedistractor plugs 290, 310 left in position in the intervertebral discspace. At this point, a further feature of the distractor plugs comesinto play. Specifically looking, for example, at the distractor plug290, the hollow stem 291, and particularly the keyed bore 301 providesan interface for a percutaneous surgical sleeve. In one embodiment, sucha sleeve 320 includes a tubular body 321 as shown in FIG. 31. Adistraction extension 322 is formed at one end of the tubular body 321.This distraction extension preferably has a height that is comparable tothe height of the elongated stem 291 so that the extension can assist inmaintaining the distracted height of the intervertebral space.

Substantially 180 degrees opposite from the distraction extension 322 isa locating spike 323. In the specific embodiment, the locating spike 323integrally extends from the end of the itubular body 321 contiguous withthe outer wall of the body. This locating spike 323 is configured toextend first through the threaded bore 302 and finally through the keyedbore 301 of the distractor plug 290. The locating spike 323 preferablyhas a shape that conforms to the shape of the keyed bore 301. In thespecific embodiment, that shape is a square, although otherconfigurations can be utilized that prevent relative rotation betweenthe distractor plug 290 and the locating spike 323. The locating spikeis preferably long enough to extend through the entire stem 291 withoutprojecting beyond the blunt end 299 of the distraction device.

The manner of use of the distractor plug and sleeve combination is shownin FIG. 32. In particular, it can be seen that a distractor plug 290 iscentrally located within the intervertebral disc space. The distractorplug 290 then serves as a locator to an anchor for the sleeve 320.Specifically, the locating spike 323 projects into the distractor plug290 into keyed engagement with the keyed bore 301. As shown in FIG. 32,the sleeve 320 is oriented to the right of the centrally disposeddistractor plug 290 so that the distraction extension 322 providesoutboard support for the distracted disc space. In this position, thesleeve 320 can then be used to perform the drilling and reamingoperations previously described particularly in connection with FIG. 21,as well as the step of inserting the fusion device as also describedabove. The curved wall 294 and curved edge 295 of the flange 292 provideclearance for insertion of the various cylindrical tools and cylindricalfusion device into the intervertebral space.

Once a fusion site has been prepared at the right side of the discspace, the sleeve 320 can be retracted, so that the locating spike 323is pulled out of the keyed bore 301 of the distractor unplug 290. Thesleeve 320 can then be rotated to the position shown in phantom in FIG.32 with the tubular body 321 directed to the left of the intervertebraldisc space. The same operations can be performed at this location in theintervertebral space. Using the distractor plug 290 and the sleeve 320,the present invention provides a means to maintain midline distractionthrough the center line of the intervertebral disc space. Moreover, thedistractor plug provides a constant fixed pivot point for the variousoperations involved in implanting an interbody fusion device.

In accordance with another embodiment of the invention, a sleeve 325 isprovided as shown in FIG. 33. In this embodiment, the sleeve 25 includesa tubular body 326 that has a distraction extension 327 projecting fromone side of one end of the sleeve. Unlike the sleeve 320, the sleeve 325includes a separate outrigger spike 328 that is fixed to the tubularbody by way of an engagement flange 329. It is understood that theoutrigger spike 328 could be integrally formed with the tubular body 326or connected to the body in some other fashion. Nevertheless, a primaryfeature of the sleeve 325 is that the spike 328 is disposed outside thediameter or outer wall of the tubular body 326. In this manner, thesleeve 325 and its hollow cannula opening can be offset further from themidline of the intervertebral disc space. Thus, interbody fusiondevices, such as device 350, can be disposed farther outboard withinthat space using the sleeve 320.

In a further embodiment, a double-barrel sleeve 330 is provided. In thisembodiment, two tubular bodies 331 and 332 are affixed at a joint 333.Each tubular body 331, 332 includes a respective distractor extension334, 335. As with the other sleeve embodiments, the distractorextensions 334, 335 have a width that approximates the width of thedistractor plug.

In this embodiment, a bore 336 is formed at the joint 333 between thetwo tubular bodies 331, 332. A spike, in the form of an elongated rod337, is configured to extend through the bore 336. This spike can thenengage a distractor plug, such as the distractor plug 310 shown in FIG.34. With this double-barrel sleeve 330, there is no need to retract thesleeve, rotated to the bilateral position and re-dispose it within adistractor plug, as in the embodiment of FIG. 32. This double-barrelsleeve 330 provides an additional distractor extension, so thatdistraction is achieved not only at the midline location of thedistractor plug 310, but also at the outboard positions of thedistractor extensions 334, 335. Again, the distractor extensions arearranged together with the distractor plug so that various percutaneousoperations can be occurring through the double-barrel sleeve of and inthe intervertebral disc space.

One problem that faces many interbody fusion devices is the risk ofbacking out or retrograde expulsion of the device. In the case ofpush-in implants, the natural compressive forces achieved by the discannulus in a distracted space can have a tendency to squeeze the fusiondevices in a retrograde direction. These same forces, coupled withrelative movement between the instrumented vertebrae, can also causethreaded fusion devices to slowly unthread. In accordance with thepresent invention, one embodiment of a fusion cage is provided that isdesigned to prevent this counter rotation of the fusion device. Thefusion device 250 shown in FIG. 8 includes a pair of bone screws thatare threaded into the adjacent vertebrae. These bone screws prevent thefusion device 250 from rotating within their prepared bores.

Another approach is presented in FIGS. 35-36. In this approach,bilaterally placed fusion devices are connected laterally across thedisc space, thereby preventing each device from rotating. In a firstembodiment shown in FIG. 35, a pair of fusion devices 350 are providedthat include a hollow body 351 having a first end 352 and a second end353. As with the fusion devices previously discussed, the devices 350each include a hollow interior 355 and an end wall 356. The devices alsoinclude external threads 358 that are adapted to be threaded into aprepared bore in adjacent vertebrae.

In a deviation from the previously discussed fusion devices, the fusiondevice 350 includes a recess 360 formed in the end wall 356. A lateralgroove 361 traverses the recess 360 and opens at the flat side walls 357of the device 350. Each device also includes a threaded bore 363centrally formed at the base of the recess 360. When each fusion device350 is placed bilaterally within an instrumented disc space, the devicesare separated by some distance, as depicted in FIG. 35. This distance isspanned by a connector plate 365. The connector plate includes anelongate arm 366 having mating ends 367 formed at the ends of the arm.Each of the mating ends 367 defines an outer wall 368 that is generallyconfigured to conform to the recesses 360 in each of the fusion devices350. The elongate arm 366 is configured to rest within the groove 361 sothat the connector plate 365 can span between and interconnect the twofusion devices 350.

The connector plate 365 is provided with a slot 369 at each of themating ends 367. This slot is oriented directly above the threaded bore363 in the end wall 356 of the fusion device 350. A locking screw 370having a threaded stem 371 is provided that extends through each slot369 and into the threaded bore 363. The locking screw 370 is thentightened into the bore to clamp the connector plate 365 to each of theinterbody fusion devices 350. Thus, the presence of the connector plate365 when disposed within the grooves 361 of the adjacent fusion devices,prevents each fusion device 350 from rotating when within the patient.The length of the connector plate 365 is dictated by the spacing of thefusion devices 350 within the disc space.

In an additional embodiment, a connector plate 375 is shown in FIG. 36.The connector plate includes an elongate arm 376 with mating ends 377,each element of which is similar to the like named elements of theconnector plate 365. However, in an alternative configuration, theconnector plate 375 includes an intermediate plate 379 that preferablyprojects perpendicularly outward from the elongate arm 376. Theintermediate plate 379 is generally in the middle of the connector plate375 and sized to sit between each of the fusion devices 350. In onespecific embodiment, the intermediate plate 379 has a width that issufficient so that the plate 379 is in contact with one side wall 357 ofthe adjacent devices 350.

In the illustrated embodiments, the focus has been on threaded fusiondevices. However, it is understood that the present invention hasutility in implanting non-threaded fusion devices, threaded andnon-threaded spacers, and cylindrical or non-cylindrical devices orplugs.

In a further aspect of this embodiment, the intermediate plate 379 isprovided with angled screw bores 380. In particular, these screw boresare angled so that a bone screw inserted through the bores can be drivenupward into the vertebral endplates of the adjacent vertebrae.Preferably, the screw bores are oriented at an angle similar to theangle of the screw bores 268 of the fusion device 250. Thus, theconnector plate 375 provides an additional degree of security to preventretrograde expulsion of the interbody fusion device 350.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

What is claimed is:
 1. An interbody fusion apparatus for implantation inthe disc space between adjacent vertebrae to be fused, comprising: ahollow body having at least an upper substantially cylindrical portionand a lower substantially cylindrical portion defining an outer diametergreater than the height of the disc space between the adjacentvertebrae, said substantially cylindrical portions each configured tocontact a portion of one of the adjacent vertebrae, said body having afirst end and an opposite second end and including an end wall at saidfirst end, said end wall defining an upper portion and a lower portion;a first screw bore defined through said end wall upper portion, saidfirst screw bore defining a first longitudinal axis oriented such thatsaid first longitudinal axis intersects said upper substantiallycylindrical portion and a second screw bore defined through said endwall lower portion, said second screw bore defining a secondlongitudinal axis oriented such that said second longitudinal axisintersects said lower substantially cylindrical portion, thelongitudinal axis of said first and second screw bores diverging fromeach other toward said second end; and a first bone screw sized toextend through said first screw bore and project outward from said uppersubstantially cylindrical portion through a first aperture and a secondbone screw sized to extend through said second screw bore and projectoutward from said lower substantially cylindrical portion through asecond aperture disposed generally opposite said first aperture, saidbone screws configured to threadedly engage the adjacent vertebrae toretain said hollow body within the disc space.
 2. The interbody fusionapparatus according to claim 1, wherein: said hollow body defines alongitudinal axis and a midline extending between said upper and lowersubstantially cylindrical portions, said midline intersecting saidlongitudinal axis, and said upper screw bore and said lower screw boreare disposed along said midline.
 3. The interbody fusion apparatusaccording to claim 1, wherein each of said two screw bores includes anenlarged recess at said end wall; and each of said two bone screwsincludes an enlarged head sized to be received within said enlargedrecess.
 4. The interbody fusion apparatus according to claim 1, whereinsaid at least two substantially cylindrical portions of said hollow bodyinclude external threads configured for threaded engagement with saidadjacent vertebrae.
 5. The interbody fusion apparatus according to claim1, wherein said hollow body is tapered from said first end to saidsecond end.
 6. The interbody fusion apparatus according to claim 1,wherein said hollow body defines two opposite substantially flat wallsbetween said at least two substantially cylindrical portions.
 7. Theinterbody fusion apparatus according to claim 1, wherein said hollowbody defines at least one slot extending through said hollow body andintersecting at least one of said substantially cylindrical portions. 8.The interbody fusion apparatus according to claim 7, wherein one of saidscrew bores intersects said at least one slot.
 9. The interbody fusionapparatus according to claim 1, wherein: said hollow body defines alongitudinal axis and a midline extending between said upper and lowersubstantially cylindrical portions, said midline intersecting saidlongitudinal axis, and said upper screw bore and said lower screw boreare disposed along said midline; and further wherein said end walldefines a pair of elongated slots offset from and substantially parallelto said midline of said end wall.-
 10. An interbody fusion apparatus forimplantation in the disc space between adjacent vertebrae to be fused,comprising: a hollow body having at least an upper substantiallycylindrical portion and a lower substantially cylindrical portiondefining an outer diameter greater than the height of the disc spacebetween the adjacent vertebrae, said substantially cylindrical portionseach configured to contact a portion of one of the adjacent vertebrae,said body having a first end and an opposite second end and including anend wall at said first end, said end wall defining an upper portion anda lower portion; a first screw bore defined through said end wall upperportion, said first screw bore defining a first longitudinal axisoriented such that said first longitudinal axis intersects said uppersubstantially cylindrical portion and a second screw bore definedthrough said end wall lower portion, said second screw bore defining asecond longitudinal axis oriented such that said second longitudinalaxis intersects said lower substantially cylindrical portion, thelongitudinal axis of said first and second screw bores diverging fromeach other toward said second end; and a first bone screw sized toextend through said first screw bore and project outward from said uppersubstantially cylindrical portion through a first aperture and a secondbone screw sized to extend through said second screw bore and projectoutward from said lower substantially cylindrical portion through asecond aperture, said bone screws configured to threadedly engage theadjacent vertebrae to retain said hollow body within the disc space:wherein said end wall of said hollow body defines a threaded borebetween said two screw bores: and wherein said apparatus includes alocking screw configured for engagement within said threaded bore, saidlocking screw having a head sized to contact each of said two bonescrews when said bone screws are extended through a respective one ofsaid two screw bores and when said locking screw is engaged in saidthreaded
 11. The interbody fusion apparatus according to claim 10,wherein each of said two screw bores includes an enlarged recess at saidend wall; each of said two bone screws includes an enlarged head sizedto be received within said enlarged recess; and said threaded boreincludes an enlarged recess sized to receive said enlarged head of saidlocking screw therein, said enlarged recess of said threaded boreoverlapping said enlarged recess of each of said bone screw bores. 12.An interbody fusion apparatus for implantation in the disc space betweenadjacent vertebrae to be fused, comprising: a hollow body having anupper substantially cylindrical portion defining a first aperture and alower substantially cylindrical portion defining a second aperturedisposed generally opposite said first aperture, said body having an endwall defining an upper portion and a lower portion; a first screw boredefined through said end wall upper portion; a second screw bore definedthrough said end wall lower portion; a first bone screw extendingthrough said first screw bore and said first aperture and into threadingengagement with one of said adjacent vertebrae: and a second bone screwextending through said second screw bore and said second aperture andinto threading engagement with an opposite one of said adjacentvertebrae.
 13. The interbody fusion apparatus according to claim 12,wherein said end wall defines a midline extending between said upper andlower portions, said upper and lower screw bores disposed along saidmidline.
 14. The interbody fusion apparatus according to claim 13,wherein said hollow body extends along a longitudinal axis, said midlineintersecting said longitudinal axis.
 15. The interbody fusion apparatusaccording to claim 12, wherein said upper and lower substantiallycylindrical portions define an outer diameter greater than the height ofthe disc space between the adjacent vertebrae.
 16. The interbody fusionapparatus according to claim 12, wherein said end wall of said hollowbody defines a threaded bore between said first and second screw bores;and wherein the interbody fusion apparatus further comprises a lockingscrew configured for threading engagement with said threaded bore andinto contact with each of said first and second bone screws.
 17. Theinterbody fusion apparatus according to claim 12, wherein said upper andlower substantially cylindrical portions include external threadsconfigured for threading engagement with said adjacent vertebrae. 18.The interbody fusion apparatus according to claim 12, wherein saidhollow body defines two substantially fiat walls arranged generallyopposite one another and extending between said upper and lowersubstantially cylindrical portions.